For instance, a glass substrate for use in a magnetic recording medium such as a hard disk (HD) to be incorporated in a hard disk drive (HDD) is manufactured by performing a glass melting step of melting a glass material; a press molding step of forming a disc-shaped glass substrate by subjecting the molten glass material to press molding in a die; a coring step of forming a center hole in the center of the glass substrate; a first lapping step of preliminarily adjusting the thickness and the flatness of the glass substrate by grinding a principal surface (recording surface) of the annular glass substrate; an end-surface grinding step of finely adjusting the outer diameter and the degree of true circle of the glass substrate by grinding an inner peripheral end surface and an outer peripheral end surface of the glass substrate; an end-surface polishing step of polishing and smoothing the inner peripheral end surface and the outer peripheral end surface of the glass substrate; a second lapping step of finely adjusting the thickness and the flatness of the glass substrate by grinding the principal surface of the glass substrate; a first polishing step (rough polishing step) of roughly polishing and smoothing the principal surface of the glass substrate; a second polishing step of finely polishing and smoothing the principal surface of the glass substrate; and a washing step of washing the glass substrate.
In addition to the above, a chemical reinforcing step of reinforcing the surface of the glass substrate, and an inspecting step of inspecting the thickness and the flatness of the glass substrate may be performed. Further, for instance, a chamfering step of chamfering the inner peripheral end surface and the outer peripheral end surface of the glass substrate may be performed in the end surface grinding step in order to suppress chipping of a corner portion between the principal surface and the end surface of the glass substrate (a surface formed by the chamfering step is called a chamfered surface).
The polishing step to be performed in a final stage in manufacturing a glass substrate is generally performed with use of a dual side polishing machine, regardless of whether the polishing step is a rough polishing step or a fine polishing step. The dual side polishing machine is provided with an upper surface plate and a lower surface plate in the form of a cylindrical column, and is configured such that surfaces of the upper surface plate and the lower surface plate facing each other are in parallel to the rotating surfaces of carriers to be described next, and the rotating directions of the upper surface plate and the lower surface plate are opposite to each other. A polishing pad is attached to each of the opposing surfaces of the upper and lower surface plates for polishing the principal surfaces of glass substrates. A number of disc-shaped carriers are disposed on the polishing pad of the lower surface plate to revolve around the rotation center of the lower surface plate, while rotating themselves. A number of circular holes are formed in each of the carriers. A glass substrate is placed in each of the circular holes. The carriers and the glass substrates are held between the polishing pads of the upper and lower surface plates, and the upper and lower surface plates and the carriers rotate in this state (all the upper and lower surface plates and the carriers are moved relative to each other). During the rotation, a polishing solution is supplied between the polishing pads and the glass substrates, whereby the glass substrates are polished.
As described in patent literature 1, a polishing pad has concave grooves for supplying a polishing solution between polishing pads and glass substrates.